Association of Glioma Grading With Inflow-Based Vascular-Space-Occupancy MRI: A Preliminary Study at 3T

On the optimization of 3D inflow-based vascular-space-occupancy (iVASO) MRI for the quantification of arterial cerebral blood volume (CBVa)

PURPOSE

The inflow-based vascular-space-occupancy (iVASO) MRI was originally developed in a single-slice mode to measure arterial cerebral blood volume (CBVa). When vascular crushers are applied in iVASO, the signals can be sensitized predominantly to small pial arteries and arterioles. The purpose of this study is to perform a systematic optimization and evaluation of a 3D iVASO sequence on both 3 T and 7 T for the quantification of CBVa values in the human brain.

METHODS

Three sets of experiments were performed in three separate cohorts. (1) 3D iVASO MRI protocols were compared to single-slice iVASO, and the reproducibility of whole-brain 3D iVASO MRI was evaluated. (2) The effects from different vascular crushers in iVASO were assessed. (3) 3D iVASO MRI results were evaluated in arterial and venous blood vessels identified using ultrasmall-superparamagnetic-iron-oxides-enhanced MRI to validate its arterial origin.

RESULTS

3D iVASO scans showed signal-to-noise ratio (SNR) and CBVa measures consistent with single-slice iVASO with reasonable intrasubject reproducibility. Among the iVASO scans performed with different vascular crushers, the whole-brain 3D iVASO scan with a motion-sensitized-driven-equilibrium preparation with two binomial refocusing pulses and an effective TE of 50 ms showed the best suppression of macrovascular signals, with a relatively low specific absorption rate. When no vascular crusher was applied, the CBVa maps from 3D iVASO scans showed large CBVa values in arterial vessels but well-suppressed signals in venous vessels.

CONCLUSION

A whole-brain 3D iVASO MRI scan was optimized for CBVa measurement in the human brain. When only microvascular signals are desired, a motion-sensitized-driven-equilibrium-based vascular crusher with binomial refocusing pulses can be applied in 3D iVASO.

Huntingtin silencing delays onset and slows progression of Huntington's disease: a biomarker study

Huntington's disease is a dominantly inherited, fatal neurodegenerative disorder caused by a CAG expansion in the huntingtin (HTT) gene, coding for pathological mutant HTT protein (mHTT). Because of its gain-of-function mechanism and monogenic aetiology, strategies to lower HTT are being actively investigated as disease-modifying therapies. Most approaches are currently targeted at the manifest stage, where clinical outcomes are used to evaluate the effectiveness of therapy. However, as almost 50% of striatal volume has been lost at the time of onset of clinical manifest, it would be preferable to begin therapy in the premanifest period. An unmet challenge is how to evaluate therapeutic efficacy before the presence of clinical symptoms as outcome measures. To address this, we aim to develop non-invasive sensitive biomarkers that provide insight into therapeutic efficacy in the premanifest stage of Huntington's disease. In this study, we mapped the temporal trajectories of arteriolar cerebral blood volumes (CBVa) using inflow-based vascular-space-occupancy (iVASO) MRI in the heterozygous zQ175 mice, a full-length mHTT expressing and slowly progressing model with a premanifest period as in human Huntington's disease. Significantly elevated CBVa was evident in premanifest zQ175 mice prior to motor deficits and striatal atrophy, recapitulating altered CBVa in human premanifest Huntington's disease. CRISPR/Cas9-mediated non-allele-specific HTT silencing in striatal neurons restored altered CBVa in premanifest zQ175 mice, delayed onset of striatal atrophy, and slowed the progression of motor phenotype and brain pathology. This study-for the first time-shows that a non-invasive functional MRI measure detects therapeutic efficacy in the premanifest stage and demonstrates long-term benefits of a non-allele-selective HTT silencing treatment introduced in the premanifest Huntington's disease.

Differential detection of metastatic and inflammatory lymph nodes using inflow-based vascular-space-occupancy (iVASO) MR imaging

PURPOSE

To investigate the potential value of inflow-based vascular-space-occupancy (iVASO) MR imaging in differentiating metastatic from inflammatory lymph nodes (LNs).

METHODS

Ten female New Zealand rabbits with 2.5-3.0 kg body weight were studied. VX2 cells and egg yolk emulsion were inoculated into left and right thighs, respectively, to induce ten metastatic and ten inflammatory popliteal LNs. Conventional MRI and iVASO were performed 2 h prior to, and 10, 20 days after inoculation (D0, D10, D20). The short-axis diameter (S), short- to long-axis diameter ratio (SLR), and arteriolar blood volume (BVa) at each time point and their longitudinal changes of each model were recorded and compared. At D20, all rabbits were sacrificed to perform histological evaluation after the MR scan.

RESULTS

The mean values of S, SLR and BVa showed no significant difference between the two groups at D0 (P = 0.987, P = 0.778, P = 0.975). The BVa of the metastatic group was greater than that of the inflammatory at both D10 and D20 (P < 0.05; P < 0.001), whereas the S and SLR of the metastatic group were greater only at D20 (P < 0.001; P = 0.001). Longitudinal analyses showed that the BVa of the metastatic group increased at both D10 and D20 (P = 0.004; P = 0.001), while that of the inflammatory group only increased at D10 (P = 0.024).

CONCLUSION

The BVa measured with iVASO has the potential to detect early metastatic LNs.

Advanced Diagnosis of Glioma by Using Emerging Magnetic Resonance Sequences

Glioma, the most common primary brain tumor in adults, can be difficult to discern radiologically from other brain lesions, which affects surgical planning and follow-up treatment. Recent advances in MRI demonstrate that preoperative diagnosis of glioma has stepped into molecular and algorithm-assisted levels. Specifically, the histology-based glioma classification is composed of multiple different molecular subtypes with distinct behavior, prognosis, and response to therapy, and now each aspect can be assessed by corresponding emerging MR sequences like amide proton transfer-weighted MRI, inflow-based vascular-space-occupancy MRI, and radiomics algorithm. As a result of this novel progress, the clinical practice of glioma has been updated. Accurate diagnosis of glioma at the molecular level can be achieved ahead of the operation to formulate a thorough plan including surgery radical level, shortened length of stay, flexible follow-up plan, timely therapy response feedback, and eventually benefit patients individually.

Decreased Muscular Perfusion in Dermatomyositis: Initial Results Detected by Inflow-Based Vascular-Space-Occupancy MRI

OBJECTIVE. This study aimed to determine whether inflow-based vascular-space-occupancy (iVASO) MRI could reproducibly quantify skeletal muscle perfusion and differentiate patients with dermatomyositis (DM) from healthy subjects. MATERIALS AND METHODS. A total of 25 patients with DM and 22 healthy volunteers underwent iVASO MRI in a 3-T MRI scanner. Maximum and mean arteriolar muscle blood volume (MBV) values of four subgroups of muscles (normal muscles, morphologically normal-appearing muscles, edematous muscles, and atrophic or fat-infiltrated muscles) were obtained. Maximum and mean arteriolar MBV values were compared among the different subgroups, and repeat testing was performed in 20 subjects to assess reproducibility. RESULTS. Compared with normal muscles in healthy subjects, morphologically normal-appearing muscles, edematous muscles, and atrophic or fat-infiltrated muscles in patients with DM showed a significant decrease of both maximum and mean arteriolar MBV (p < .001). Both parameters were significantly lower in atrophic or fat-infiltrated muscles than in morphologically normal-appearing and edematous muscles (p < .001). ROC AUCs for discriminating patients with DM from healthy volunteers were 0.842 and 0.812 for maximum and mean arteriolar MBV values, respectively. As a measure of test-retest studies, the intraclass correlation coefficients (ICCs) were 0.990 (95% CI, 0.986-0.993) and 0.990 (95% CI, 0.987-0.993) for maximum and mean arteriolar MBV, respectively. For interobserver reproducibility, the ICCs were 0.989 (95% CI, 0.986-0.991) and 0.980 (95% CI, 0.975-0.983), respectively. CONCLUSION. iVASO MRI can reproducibly quantify arteriolar MBV in the thigh and discriminate between healthy volunteers and patients with DM.

The Added Value of Inflow-Based Vascular-Space-Occupancy and Diffusion-Weighted Imaging in Preoperative Grading of Gliomas

OBJECTIVES

The present study aimed to study whether combined inflow-based vascular-space-occupancy (iVASO) MR imaging (MRI) and diffusion-weighted imaging (DWI) improve the diagnostic accuracy in the preoperative grading of gliomas.

METHODS

Fifty-one patients with histopathologically confirmed diffuse gliomas underwent preoperative structural MRI, iVASO, and DWI. We performed 2 qualitative consensus reviews: (1) structural MR images alone and (2) structural MR images with iVASO and DWI. Relative arteriolar cerebral blood volume (rCBVa) and minimum apparent diffusion coefficient (mADC) were compared between low-grade and high-grade gliomas. Receiver operating characteristic (ROC) curve analysis was performed to compare the tumor grading efficiency of rCBVa, mADC, and the combination of the two parameters.

RESULTS

Two observers diagnosed accurate tumor grade in 40 of 51 (78.4%) patients in the first review and in 46 of 51 (90.2%) in the second review. Both rCBVa and mADC showed significant differences between low-grade and high-grade gliomas. ROC analysis gave a threshold value of 1.52 for rCBVa and 0.85 × 10-3 mm2/s for mADC to provide a sensitivity and specificity of 88.0 and 81.2% and 100.0 and 68.7%, respectively. The area under the ROC curve (AUC) was 0.87 and 0.85 for rCBVa and mADC, respectively. The combination of rCBVa and mADC values increased the AUC to 0.92.

CONCLUSION

The combined application of iVASO and DWI may improve the diagnostic accuracy of glioma grading.

Noninvasive Assessment of O(6)-Methylguanine-DNA Methyltransferase Promoter Methylation Status in World Health Organization Grade II-IV Glioma Using Histogram Analysis of Inflow-Based Vascular-Space-Occupancy Combined with Structural Magnetic Resonance Imaging

BACKGROUND

O(6)-methylguanine-DNA methyltransferase (MGMT) promoter methylation is an important prognostic factor for gliomas and is associated with tumor angiogenesis. Arteriolar cerebral blood volume (CBVa) obtained from inflow-based vascular-space-occupancy (iVASO) magnetic resonance imaging (MRI) is assumed to be an indicator of tumor microvasculature. Its preoperative predictive ability for MGMT promoter methylation remains unclear.

PURPOSE

To investigate the role of iVASO-CBVa histogram features in determining MGMT promoter methylation status of grade II-IV gliomas.

STUDY TYPE

Retrospective SUBJECTS: Forty-six patients consisting of 20 MGMT methylated and 26 unmethylated gliomas.

FIELD STRENGTH/SEQUENCE

3.0 T magnetic resonance images containing iVASO MRI, T₁ -weighted image (T₁ WI), T₂ -weighted image, T₂ -weighted fluid attenuated inversion recovery image images, and enhanced T₁ WI.

ASSESSMENT

Sixteen structural imaging features were visually evaluated on structural MRI and 14 CBVa histogram features were extracted from iVASO-CBVa maps.

STATISTICAL TESTS

Imaging features were screened and ranked using Fisher's exact test, Mann-Whitney U-test, and randomforest algorithm. Features with higher importance were selected to develop logistic regression models to determine MGMT methylation status. Receiver operating characteristics (ROC) curve with the area under the curve (AUC) and leave-one-out cross-validation (LOOCV) were used to assess effectiveness and stability.

RESULTS

The top two CBVa histogram features were root mean squared (RMS) and variance. The top two structural imaging features were contrast-enhancing component of the tumor (CET) location and tumor location. Both the CBVa model of RMS and variance (ROC, AUC = 0.867; LOOCV, AUC = 0.819) and the model of structural features (ROC, AUC = 0.882; LOOCV, AUC = 0.802) accurately identified MGMT methylation. The fusion model of CBVa RMS and CET location improved diagnostic performance (ROC, AUC = 0.931; LOOCV, AUC =0.906). DATA CONCLUSION: iVASO-CBVa has potential in evaluating MGMT methylation status in grade II-IV gliomas.

LEVEL OF EVIDENCE

4 TECHNICAL EFFICACY: Stage 2.

Mutant G2019S-LRRK2 Induces Abnormalities in Arteriolar Cerebral Blood Volume in Mouse Brains: An MRI Study

BACKGROUND

Parkinson's disease (PD) is the second most common neurodegenerative disease and the most common movement disorder characterized by motor impairments resulting from midbrain dopamine neuron loss. Abnormalities in small pial arteries and arterioles, which are the primary pathways of local delivery of nutrients and oxygen in brain tissue, have been reported in many neurodegenerative diseases including PD. Mutations in LRRK2 cause genetic PD and contribute to sporadic PD. The most common PD-linked mutation LRRK2 G2019S contributes 20-47% of genetic forms of PD in Caucasian populations. The human LRRK2 G2019S transgenic mouse model displays PD-like movement impairment and was used to identify novel LRRK2 inhibitors, which provides a useful model for studying microvascular abnormalities in PD.

OBJECTIVES

To investigate abnormalities in arteriolar cerebral blood volume (CBVa) in various brain regions using the inflow-based vascular-space occupancy (iVASO) MRI technique in LRRK2 mouse models of PD.

METHODS

Anatomical and iVASO MRI scans were performed in 5 female and 7 male nontransgenic (nTg), 3 female and 4 male wild-type (WT) LRRK2, and 5 female and 7 male G2019S-LRRK2 mice of 9 months of age. CBVa was calculated and compared in the substantia nigra (SN), olfactory cortex, and prefrontal cortex.

RESULTS

Compared to nTg mice, G2019S-LRRK2 mice showed decreased CBVa in the SN, but increased CBVa in the olfactory and prefrontal cortex in both male and female groups, whereas WT-LRRK2 mice showed no change in CBVa in the SN (male and female), the olfactory (female), and prefrontal (female) cortex, but a slight increase in CBVa in the olfactory and prefrontal cortex in the male group only.

CONCLUSIONS

Alterations in the blood volume of small arteries and arterioles (CBVa) were detected in the G2019S-LRRK2 mouse model of PD. The opposite changes in CBVa in the SN and the cortex indicate that PD pathology may have differential effects in different brain regions. Our results suggest the potential value of CBVa as a marker for clinical PD studies.